Water-soluble polymers can be prepared in several forms. For instance, it is known in the art that water-soluble polymers can be dispersed in the oil phase of water-in-oil emulsions. Conventional water-in-oil emulsion polymerization techniques generally involve forming a water-in-oil emulsion of an aqueous solution of at least one water-soluble ethylenically unsaturated monomer in an inert hydrophobic liquid organic dispersion medium and polymerizing the monomer or monomers in the dispersion medium to form a polymer emulsion.
In such polymerization methods, virtually any polymerizable ethylenically unsaturated water-soluble monomer can be polymerized and dispersed into a water-in-oil system. Thus, anionic, cationic, nonionic, and amphoteric emulsion polymers can be prepared by conventional emulsion polymerization techniques.
Water-in-oil emulsions generally include three primary components: (1) a hydrophobic or oil phase; (2) an aqueous phase; and (3) a surfactant system. The oil phase generally makes up from 5 to 75%, by weight, of the emulsion. Any inert hydrophobic liquid can be used as the oil phase. Typical hydrophobic liquids include, but are not limited to, benzene, xylene, toluene, mineral oils, kerosene, napthas, petroleums, petroleum distillates, branch-chain hydrocarbons, branch-chain isoparaffinic hydrocarbons, and blends of aromatic and aliphatic hydrocarbons containing 4 or greater carbon atoms.
The aqueous phase generally accounts for from 25 to 95% by weight of the emulsion. This phase contains the desired ethylenically unsaturated monomer or monomers and water. Additionally, this phase may contain an effective amount of a chelating agent, such as a sodium salt of ethylene diamine tetraacetic acid (EDTA) or nitrilotriacetate (NTA), buffers, chain transfer agents, or other additives. The monomer(s) to be polymerized typically make up about 10 to about 60% by weight of the aqueous phase, with the balance being primarily water.
The surfactant system generally makes up 0.5 to 20% by weight of the emulsion. Any surfactant system which effectively disperses an aqueous phase into a hydrophobic phase can be used. See, for example, U.S. Pat. No. 3,826,771, which discloses the use of sorbitan monooleate as a water-in-oil emulsifying agent; U.S. Pat. No. 3,278,506, which discloses the use of ethylene oxide condensates of fatty acid amides as emulsifiers; U.S. Pat. No. 3,284,393, which discloses the use of hexadecyl sodium phthalate, sorbitan monooleate, sorbitan monostearate, cetyl or stearyl sodium phthalate and metal soaps as water-in-oil emulsifiers; and U.S. Pat. No. 4,024,097, which discloses the use of surfactant systems comprising an oil-soluble alkanolamide, as well as one or more co-emulsifiers selected from unesterified dialkanol fatty amides, quaternized ammonium salts of fatty tertiary amines, salts of fatty tertiary amines, alkaline metal salts of fatty acids, and alkyl or alkylaryl sulfates or sulfonates.
Emulsion polymers are generally produced by first mixing the surfactant system with the hydrophobic phase. The aqueous phase is then typically prepared by adding the monomer(s) to water in the desired concentration. Additionally, a chelant, such as a sodium salt of EDTA, may be added to the aqueous solution and the pH of the aqueous phase may be adjusted to between about 3.0 and 10.0, depending on the monomer(s) used. The aqueous monomer phase is then added to the mix containing the hydrophobic liquid and the surfactant system. The surfactant system enables the aqueous phase, which contains the monomer or monomers to be polymerized, to be emulsified into the hydrophobic phase. Polymerization is then carried out in the presence of a free radical generating catalyst, and the temperature of the reaction mixture is generally maintained between about 5° C. and about 100° C., resulting in a water-in-oil emulsion polymer. Any type of free radical initiator can be used including, for example, persulfate and azo initiators. High-energy irradiation can also be used to initiate polymerization.
The following patents provide further background relative to the manufacture of emulsion polymers or for the application of polymers in combination with microparticles for enhanced process performance.
U.S. Pat. No. 3,041,318 to Hess discloses emulsifying an aqueous dispersion of a polymer prepared from a compound containing a polymerizable ethylenically unsaturated group into a water-in-oil emulsion, and then precipitating the polymer therefrom as discrete particles.
U.S. Pat. No. 3,284,393 to Vanderhoff et al. discloses a water-in-oil emulsion polymerization process wherein a water-soluble monomer is emulsified in an oil phase and polymerized therein, resulting in a polymeric latex which is then separated from the reaction medium.
U.S. Pat. No. 4,579,667 to Echt et al. discloses gelled aqueous compositions containing an anionic partially hydrolyzed polyacrylamide and a water-soluble cationic polyamide-epihalohydrin resin useful in fracturing oil and gas formations in enhanced oil recovery. The polymers can be prepared by solution polymerization, precipitation polymerization, water-in-oil emulsion polymerization, and water-in-oil suspension polymerization. The gels can be used to suspend propping agents, to reduce water loss by serving as a plugging agent, and as a “pusher” in surfactant flooding.
U.S. Pat. No. 6,488,091 to Weaver et al. discloses subterranean formation treating fluid concentrates that include water and a substantially fully hydrated depolymerized polymer. The treating fluids which are formed by adding water to the treating fluid concentrates include water, a substantially fully hydrated depolymerized polymer, and a crosslinking agent for crosslinking the hydrated depolymerized polymer.
U.S. Pat. No. 6,454,902 to Chen discloses a process for making paper by forming a cellulosic suspension, flocculating the suspension, draining the suspension on a screen to form a sheet and then drying the sheet. The cellulosic suspension is flocculated by addition of a water-soluble polymer which is selected from a polysaccharide or a synthetic polymer of intrinsic viscosity of at least 4 dl/g and then reflocculated by a subsequent addition of a reflocculating system, wherein the reflocculating system comprises a siliceous material and a water-soluble polymer.
U.S. Pat. No. 6,413,433 to Maury et al. discloses a process for dewatering sludge that contains solids and water. The method includes the steps of adding a cationic dispersion polymer and a microparticle to the sludge, where the cationic dispersion polymer can be added before or after or simultaneously with the addition of the microparticle, and physically separating the solids from said water.
Although there are numerous applications where water-soluble polymers are added to treat aqueous systems in conjunction with various microparticles, the methods are cumbersome because they require separately feeding a polymer and a microparticle to a system. It would be highly desirable to add the microparticle and the polymer in a single composition that could be prepared prior to use and be able to be stored prior to use for a reasonable period of time.